The present invention relates to magnetostriction, more particularly to the utilization of positive magnetostrictive materials while being subjected to mechanical stresses.
The so-called “active materials” include magnetostrictives (e.g., Terfenol-D), electrostrictives, piezoelectrics (e.g., PZT, PMN-PT), and shape memory alloys (acronym, “SMA”). Active materials are used as sensors and actuators in various devices (such as smart structures) that integrate active and passive material systems. Typically, the active material system is subjected to significant mechanical stresses during operation of the device. With the notable exception of the recently discovered Galfenol class of alloy, modern active materials (e.g., Terfenol-D, PZT, PMN-PT) are robust under compressive stress but break relatively easily when a tensile stress is applied. Iron-gallium (Fe-Ga) alloys known as “Galfenol,” newly developed by the United States Navy's Naval Surface Warfare Center, Carderock Division, are materials that have large positive magnetostrictions but that are strong in both compression and tension. Certain other magnetostrictive materials, such as aluminum alloys, exhibit varying degrees of robustness in response to tensile stress; however, Galfenol is superior to all other magnetostrictive materials in this respect by at least a factor of two.
In a magnetostrictive material, the dimensions change as the material's magnetization direction varies. According to conventional practice involving magnetostriction, a magnetic field is applied to a magnetostrictive material to manipulate the material's magnetization direction. The magnetization direction tends to align itself parallel to the applied magnetic field. The magnetostrictive material acts as a transducer or motor, converting electrical to mechanical energy. A “positive” magnetostrictive material (i.e., a material that is characterized by “positive” magnetostriction) is one that, while subjected to longitudinally-axially directed compressive stress, expands (e.g., enlarges or lengthens) in the longitudinal-axial direction when then placed in a longitudinally-axially directed magnetic field created by an electrically conductive coil circumferentially circumscribing the magnetostrictive material; in the case of a positive magnetostrictive material, its magnetization shifts from transversely directed side-by-side orientation (brought about by the longitudinally-axially directed compressive stress) to longitudinally-axially directed end-to-end orientation (brought about by the longitudinally-axially directed magnetic field). A “negative” magnetostrictive material (i.e., a material that is characterized by “negative” magnetostriction) is one that, while subjected to longitudinally-axially directed tensile stress, contracts (e.g., shrinks or shortens) in the longitudinal-axial direction when then placed in a longitudinally-axially directed magnetic field created by an electrically conductive coil circumferentially circumscribing the magnetostrictive material; in the case of a negative magnetostrictive material, its magnetization shifts from transversely directed orientation (brought about by the longitudinally-axially directed tensile stress) to longitudinally directed end-to-end orientation (brought about by the longitudinally-axially directed magnetic field).
Positive magnetostriction materials are traditionally used with compressive stresses. Although heretofore unrealized, it would be desirable in many contexts to use positive magnetostriction materials with tensile stresses. The recent advent of Galfenol has whetted the technological world's appetite for such capabilities. For instance, one can contemplate various kinds of active apparatus that would prove useful in sonar, vibration damping, and other application. To achieve this goal, however, magnetic manipulation techniques commonly applied when using positive magnetostriction materials with compressive stresses would prove rather awkward to effectuate when using positive magnetostriction materials with tensile stresses.
The following references, incorporated herein by reference, are informative regarding magnetostriction in general, and Galfenol in particular. Wun-Fogle et al. U.S. Pat. No. 6,139,648 issued 31 Oct. 2000, entitled “Prestress Imposing Treatment of Magnetostrictive Material”; Wun-Fogle et al. U.S. Pat. No. 6,176,943 B1 issued 23 Jan. 2001, entitled “Processing Treatment of Amorphous Magnetostrictive Wires”; “Tensile Properties of magnetostrictive Iron-Gallium Alloys,” R. A. Kellogg, A. M. Russell, T. A. Lograsso, A. B. Flatau, A. E. Clark and M. Wun-Fogle, Acta Materialia, vol. 52, pp 5043-5050 (available online 25 Aug. 2004 at www. sciencedirect.com); “Extraordinary Magnetoelasticity and Lattice Softening in b.c.c. Fe-Ga Alloys,” A. E. Clark, K. B. Hathaway, M. Wun-Fogle, J. B. Restorff, T. A. Lograsso, V. M. Keppens, G. Petculescu, and R. A. Taylor, Journal of Applied Physics, vol. 93, no. 10, pp 8621-8623 (15 May 2003); “Texture and Grain Morphology Dependences of Saturation Magnetostriction in Rolled Polycrystalline Fe83Ga17,” R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, and T. A. Lograsso, Journal of Applied Physics, vol, 93, no. 10, pp 8495-8497 (15 May 2003); “Structural Transformations in Quenched Fe-Ga Alloys,” T. A. Lograsso, A. R. Ross, D. L. Schlagel, A. E. Clark and M. Wun-Fogle, Journal of Alloys and Compounds, vol. 350, pp 95-101 (17 Feb. 2003); Magnetostrictive Properties of Galfenol Alloys under Compressive Stress,” A. E. Clark, M. Wun-Fogle, J. B. Restorff, and T. A. Lograsso, Materials Transactions, vol. 43, no. 5, pp 881-886, The Japan Institute of Metals, Special Issue on Smart Materials—Fundamentals and Applications (2002); “Temperature and Stress Dependence of the Magnetic and Magnetostrictive Properties of Fe81Ga19,” R. A. Kellogg, A. Flatau, A. E. Clark, M. Wun-Fogle and T. A. Lograsso, Journal of Applied Physics, vol. 91, no. 10, pp 7821-7823 (15 May 2002); “Magnetostriction of Ternary Fe-Ga-X Alloys (X=Ni, Mo, Sn, Al),” J. B. Restorff, M. Wun-Fogle, A. E. Clark, T. A. Lograsso, A. R. Ross, and D. L. Schlagel, Journal of Applied Physics, vol. 91, no. 10, pp 8225-8227 (15 May 2002); “Effect of Quenching on the Magnetostriction of Fe1-xGax (0.13<x<0.21),” A. E. Clark, M. Wun-Fogle, J. B. Restorff, T. A. Lograsso and J. R. Cullen, IEEE Transactions on Magnetics, vol. 37, no. 4, pp 2678-2680 (July 2001); “Magnetoelasticity of Fe-Ga and Fe-Al Alloys,” J. R. Cullen, A. E. Clark, M. Wun-Fogle, J. B. Restorff and T. A. Lograsso, Journal of Magnetism and Magnetic Materials, vols. 226-230, part 1, pp 948-949 (May 2001); “Magnetostrictive Properties of Body-Centered Cubic Fe-Ga and Fe-Ga-Al Alloys,” Arthur E. Clark, James B. Restorff, Marilyn Wun-Fogle, Thomas A. Lograsso and Deborah L. Schlagel, IEEE Transaction on Magnetics, vol. 36, no. 5, pp 3238-3240 (September 2000); “Magnetostrictive Galfenol/Alfenol Single Crystal Alloys Under Large Compressive Stresses,” A. E. Clark, M. Wun-Fogle, J. B. Restorff, and T. A. Lograsso, Proceedings of Actuator 2000, 7th International Conference on New Actuators, Bremen, Germany, 19-21 Jun. 2000, pp 111-115; “Strong, Ductile, and Low-Field-Magnetostrictive Alloys Based on Fe-Ga,” S. Guruswamy, N. Srisukhumbowornchai, A. E. Clark, J. B. Restorff, and M. Wun-Fogle, Scripta Materialia, vol. 43, issue 3, pp 239-244 (20 Jul. 2000).